Tissue joining and sealing utilizing sutures and staples is the keystone in modern surgical procedures. An alternative approach utilizes a laser to expose a glue or solder to thereby join adjacent tissues. In many respects, such laser assisted tissue soldering is superior to conventional suture or staple-based methods. The advantages are speed, reduced infection, acceleration in healing, better cosmetic appearance and ease of use particularly in laparoscopic surgery where water tightness and limited access or small size of the repair are important. Laser assisted tissue welding often requires glues or solders for promoting strong bonds, forming a bridge between two apposed tissue sections. The ideal solder is chemically and mechanically matched to the tissue. As a result the solder is strong but stretches and grows with the tissue because of good modulus match. Chromophores mixed with the solder can assist in confining the deposited energy and reduce the impact of tissue imperfections. These additives, however, may be toxic and cause pernicious effects.
The need to provide reliable sutureless closures is paramount to reducing morbidity and mortality rates and lowering health care costs. Achieving complete anastomotic integrity without damaging native tissues will provide the general surgeon with a very powerful tool. For example, laser assisted tissue welding can be used in heart surgery to repair congenital defects thereby eliminating blood loss, the main cause of mortality in these procedures. Tissue welding can also benefit patients with coagulation abnormalities, those suffering from dissection of the aorta and those undergoing minimally invasive coronary artery by-pass grafting (CABG). Laser assisted anastomoses will prevent post-operative leakage in bowel and esophageal repair. It will provide a means for repairing damage to articular cartilage, a common problem affecting joints of millions of people. Sutureless transplantation of osteochondral autografts can reduce pain and recovery time and eventually eliminate the need for total joint replacement. The use of a solder will further reduce dead spaces between circular grafts and provide a bridge for optimizing the different mechanical properties of donor to recipient hyaline cartilage. Laser assisted tissue welding can also be used to repair meniscal and treat osteoarthritis and spinal disc injuries and are among other applications of this invention.
Methods reported to date have not gained clinical acceptance. The major reasons include the high level of surgeon skill that is required, the strength, toxicity and resorbability of the tissue solder, the potential for irreparable laser damage and cost of the laser system.
Consistent with the present invention, a suitable solder and associated laser welding system are provided which avoid the shortcomings of conventional systems described above. For example, the biological solders and sealants consistent with the present invention are biodegradable and do not require chormophores or dyes to promote adhesion. Further, consistent with the present invention, the laser system provides accurate temperature control to eliminate peripheral tissue damage, damage to stay sutures (if required), and large area exposure to reduce treatment time. Further, the use of a feedback controller reduces required surgeon skill. The laser system can be comprised of inexpensive off-the-shelf components and has been designed to be compact, nonintrusive in a surgical setting, inexpensive to manufacture and user friendly.
It is believed that the laser energy disrupts the three-dimensional structure of collagen fibers found in tissues, promoting tissue crosslinking and improving cohesive strength. The films or gels are easy to apply and fix to the tissue surface.
Further consistent with the present invention, a method is provided for preparing suitable protein compositions for use with the laser system. The compositions are comprised of chemically derivatized soluble collagen, which is formulated to concentrations ranging from 300 mg/ml (30%) to 800 mg/ml (80%) collagen protein. In particular, Type I collagen, for example, is first prepared by extraction from animal hide, skin or connective tissue and purified. The collagen preparations are then chemically derivatized with sulfhydryl reagents to improve cohesive strength and with secondary derivatizing agents, such as carboxyl groups, to improve the adhesive strength of the solder to the tissue. The compositions are then formed into liquid, gels or solid films which when exposed to energy generated from an infrared laser, for example, undergo thermally induced phase transitions. Solid or semi-solid protein compositions become less viscous enabling the high concentration protein to penetrate the interstices of treated biological tissue or to fill voids in tissue. As thermal energy is released into the surrounding environment, the protein compositions again become solid or semi-solid, adhering to the treated tissue or tissue space.
In accordance with an additional feature of the present invention, minute quantities of any derivative of commercially available, medical grade cyanoacrylate can be applied to fix and appose tissue edges. Next a layer of the high concentration collagen can be applied adjacent to and on the surface of the tissue to be bonded. This top layer is typically exposed to a infrared laser to melt, denature, and mix the two components to promote both chemical and mechanical bonds to the tissue as well as enhancing intrinsic strength of the composite solder. Infrared laser exposure increases temperature at the bonding site. Feedback control of the laser can be used to adjust solder temperature for optimizing the bonding mechanism to the tissue while preventing thermal damage to adjacent healthy tissue.
It is believed that high concentration collagen compositions described in this invention have an increased volume of linkages to improve the strength performance of the solder while modulating the thermal melt temperatures and solder viscosities. Laser exposure parameters were chosen to rapidly flow the solder and promote physical contact of the solder with the tissue. These parameters include choice of an operating wavelength in the infrared range, power density, pulsed or cw mode, exposure times and tissue temperature. The following examples are illustrative of the invention but are not intended to limit the scope thereof.